Drop out fuse switch



Oct, 13, 1953 w. G. MILNE ET AL 2,655,576

' DROP OUT FUSE SWITCH Filed April 15, 1953 Fir .1 56

'tion.

Patented Oct. 13, 1953 2,655,576 DROP u FUSE SWITCH Winford G. Milne,Hamilton, Ontario, and Reginald E. Jones, Toronto, Ontario, Canada,assignors to N. Slater Company Limited, JHamilton, Ontario, CanadaApplication April 15, 1953, Serial .No. 349,074 6 Claims. (01. 200 114)This invention relatesto drop outfuseswitches.

As is known, such switches are used for disconnecting transformers orlocal circuits, from a main power feed.

Usually, such a switch essentially consists of an insulated uppercontact to which the 'feed wire is attached, and an insulated lowercontact'to which the transformer or secondary circuit is attached, afuse serving electrically to connect the upper and lower contacts. Thefuse isenclosed in a rigid insulating tube. The tube, with the fuseenclosed therein, in effect forms a switch member which electricallyconnects the two contacts. Upon an overload occurring in the circuit,the fuse burns out and the tube dropsdown, describing an arc of roughly180. When the switch member has swung dowmaspreviously-described, it ismanually removed and the blown fuse replaced by a new one insertedintothe tube, and the switch member returned to operative posi- VVhenthe switch member is manipulated to break the circuit, the member veryoften draws a most destructive are which not only is injurious to theswitch itself, but will sometimes spread to adjacent switches mounted inits proximity.

The main object of this invention, therefore, is to provide a switch ofthe type hereinbefore described, which can be opened manually withoutdanger or hazards of drawing a destructive are.

In the drawing:

Figure 1 is a front view of the drop out fuse switch in circuit closedposition. Figure 2 is'an elevation of the lower portion of the assemblyof Figure l.

Referring now by numerals to the drawing, there are shown twoconventional insulators, l0 and H, suspended by a conventional cross arm(not shown) by means of a conventional supporting bracket B (shown inpart only) Supported. by the upper end of the insulator I0 is aresilient contact bracket I2, which takes the form of relatively stifiround wire in two identical parallel spaced strands (secondstrand notshown). The contact bracket is supportedby a lug 3 rigidly extendingfrom one complementary element of a two-piece clamp 20. The contactbracket is secured to the lug l3 as by a clamping member [4 bolted tothe lug, and is electrically connected to a lead (not shown) by aconventional connector I 6. The outer or free .end of each strand of thecontact bracket is formed with an offset or arched portion llterminating in divergent horns l8. w

Suspended from the lower end of the insulator H is a hinge bracket 2|.The hinge bracket is Secured by a bolt 24 to a lug 22 rigidly extendingfrom one complementary element of a twopiece clamp 23. The hinge bracket2! and the contact bracket I2 aforesaid also have associated with themthe two terminals of the switch. The switch proper (more specifically tobe referred to later), serves to complete the circuit between the twoterminals.

The switch proper, shown as 3SA, includes a crank presenting twoangularly-disposed legs or levers 28 and 21, and pivots 28 journalled inthe hinge bracket 21 so that the crank is mounted for rotary movement onthe axis of the pivots. The leg 21 carries astud 29 on which is threadeda nut 30.

Such a switch includes a fuse comprising a tube 3|, made of a toughinsulating material, usually Bakelite, carryin'ga topcontact member 34having a U-shaped lug 33 adapted electrically to engage the arcuateportions I! of the contact bracket 12. The lower end of the tube carriesa clamp 36, one end of which is pivotally connected to the upper end ofthe leg 26 as by a pin 31.

Enclosed within the tube 3| is a fusible element (not shown) interposedbetween an upper pigtail (not shown) electrically connected to the "topcontact member 33, and a lower pigtail 38 which projects through thelower end of the tube 3| and is electrically connected to the leg 21 ofthe crank by being clamped between the leg 27 and the nut 30. Thus, whenthe switch proper is closed, the circuit between the resilient contactbracket 12 and the hinge bracket 2| is closed.

The arrangement of clamp 36, and crank, the leg 21 of which is in efiecttied to the tube-3l (more particularly, being tied to the lower pigtail38) is such that the tube is retained in its normal or circuit-closingposition, as shown in Figure 1. When an overload occurs in the circuit,the fusible element blows out. This allows the lower pigtail 38 todropbeing aided by the i volume of hot gas generated withinthe tube 3l-"hinge bracket 2|, bodily to lower the tube and allowing the crank torotate clockwise on the cause the disengagement of thecontact 33 fromthe contact bracket [2. The tube will swing outwardly in an arc of acircle, and hang vertically from the hinge bracket. The blown-out orexpended switch proper or fuse issubsequently removed and replaced'by anew one.

' The arched portion ll of the contact bracket 12 is so formed'that whenthe switch is closed as in Figure 1, the bracket is retained in suchposi 3 tion, until the fuse blows out Or the switch is opened manually.

Conveniently, the tube 31 carries an eye 39 by which the fuse, whenhanging from the hinge bracket 2|, may be swung upwardly into closedposition as by a suitable insulated pole (not shown). Such tube, moreparticularly the clamp contact 36, carries a rigid lever or lug 4! toassist in the manipulation of the switch from the ground by theinsulated pole.

The drop out fuse switch thus far described is a conventional one, andno claim is made thereto. 7

Such a switch serves not only as a fuse, but as a switch properlyspeaking, that is, a switch which is to be opened and closed as desired,to make and break the circuit between the switch terminals. When theswitch is being opened, as already stated, the switch member often drawsa most destructive arc. On the other hand, a switch according to thisinvention, now to be described, prevents the occurrence of anysubstantial or injurious arc.

Extending from the cl mp 3t, a portion 42, conveniently of a rectangularcross section. The portion 42 is so directed relatively to the clamp 36as to be more or less generally parallel with the axis of the tube (ii.

Secured to the portion 42, as by a suitable twopiece clamp i l, is aresilient or flexible contact C. The contact preferably takes the formof four thin metal bars or leaves. Two such bars or leaves E and iel-lof unequal length, are disposed cn one side of the portion 52, while theother two bars or leaves and A, also of unequal length, are disposed onthe opposite side of the portion :32. The upper or free end of the barQSA is preferably provided with a rounded contact head 31'. 12 structurecomprising these bars is essentially the equivalent of a multiple leafspring, the two pairs of leaves being spaced apart except for a tipengagement between the longer member of one pair with the shorter memberof the other pair.

A flexible contact arm C made as shown, that is, comprising fourseparate members, or two pairs, has many advantages. Such membersgenerate friction, such generated friction tending to reduce resonantvibrations which will often occur when the contact is exposed to windsof high velocity and conceivably might cause the upper end of the switchcontact to come into contact with parts of the switch.

Disposed to lie in the path of spring contact C, more particularly inthe path of the end portion or head 4-? of the contact arm C, is alatching device. Ihe latching device may take the form shown, that is alever 52 is pivotally suspended as by pin 5-1 from a pair of spacedparallel lugs 48 rigidly extending from one end of one complementaryelement of a two-piece clamping device so clamped to the contact bracket2 as by a bolt The outer ends of the lugs d2 are each provided withdown-turned lips or stops 5%, forming abutments or shoulders adapted tobe engaged by the iatcl lever to determine or limit its anti-clockwiserotation as seen in Figure 1. The lever on the other hand, is free torotate clockwise. Thus, as the contact C swings downwardly (clockwise)with the tube 3! it engages the levcr 52 of the latching device and isrestrained from further movement until the switch contact C (moreparticularly its member 53A) has flexed sumciently to slide over and bereleased from the lever 52. The arrangement is such that before thecontact C is free of the latch or lever 52, the fuse, more particularlythe contact 33 of the fuse, is out of contact with the bracket [2 and issufiiciently spaced therefrom to prevent arcing between the bracket 12and the fuse contact member 33. The arrangement is also such that whenthe fuse is rotated anticlockwise, again to make or close the circuit,the contact arm C moves or swings the latch out of its path, whereuponelectrical contact is made with the bracket I2, when the part A! willhave cleared the latch or lever 52, and the latter having dropped bygravity anti-clockwise in to contact with the stops or shoulders 56.

We claim:

1. In a drop out fuse switch of the kind described including a resilientcontact bracket and a hinge bracket forming the terminals of the switch,a switch arm comprising an insulating tube, a top contact member carriedby said tube for electrical engagement with said resilient contactbracket, a crank pivotally supported by said hinge bracket, a conductorincluding a fusible element within said tube electrically connectedbetween said top contact member and said crank, aclamp carried by saidtube and having a portion pivotally supported by said crank, thearrangement being such that said switch arm drops and swings open tobreak the circuit between the terminals when said fusible element blowsout under an overload; the improvement comprising, spring conductormeans secured to a conductor member associated with said tube bodily tomove therewith, a latching device electrically connected to saidresilient contact bracket and lying in the path of said spring means tobe engaged thereby as said tube is swung toward circuitbreaking positionand to retain said engagement until the circuit has been effectivelybroken between said terminals of the switch, said latching deviceoperating to permit unimpeded return of said spring means with said tubeto circuitmaking position.

2. In a drop out fuse switch of the kind described including a resilientcontact bracket and a hinge bracket forming the terminals of the switch,a switch arm comprising an insulating tube, a top contact member carriedby said tube for electrical engagement with said resilient contactbracket, a crank pivotally supported by said hinge bracket, a conductorincu a fusible element within said tube electrically onnected betweensaid top contact member and said crank, a clamp carried by said tube andhaving a portion pivotally supported by said crank, the arrangementbeing such that said SwlLCh arm drops and swings open to break thecircuit between the terminals when said fusible element blows out underan overload; the improvement comprising, a resilient flexible contactarm secured at its lower end to a portion of said clamp and rising inspaced relationship to said tube bodily to move therewith, a latchingdevice electrically connected to said resilient contact bracket andlying in the path of the free end of said resilient flexible contact armto be engaged by said free end as said tube is swung towardcircuitbreaking position and to retain said free end in contacttherewith until the circuit has been effectively broken, between saidterminals of the switch, said latch operating to permit unimpeded returnof said arm with said tube to circuitmaking position.

3. A drop out fuse switch as in claim 2, said resilient flexible contactarm comprising a leaf spring having an upper portion for engagement withsaid latching device and a plurality of tensioned leaf springs ofunequal lengths effectively retaining said first leaf spring in flexedtensioned condition.

4. A drop out fuse switch as in claim 2, the resilient flexible contactarm comprising a pair of leaf springs of unequal lengths, the longer ofsaid leaf springs having an upper portion for engagement with saidlatching device, and a second pair of tensioned leaf springs of unequallengths for effectively retaining said first pair of leaf springs inflexed tensioned condition, the longer leaf spring of said second pairtensionally engaging the shorter leaf spring of said first pair.

5. A drop out switch as in claim 2, the resilient flexible contact armcomprising a pair of leaf springs of unequal lengths, the longer of saidleaf springs having an upper portion for engagement with said latchingdevice and a second pair of tensioned leaf springs of unequal lengthsfor effectively retaining said first pair of leaf springs in flexedtensioned condition, the tip of the longer leaf spring of said secondpair tensionally engaging the shorter leaf spring of said first pair,said pairs being wholly spaced apart except for said engagement of saidtip.

6. A drop out fuse switch as in claim 2, the re silient flexible contactarm comprising two leaf springs of unequal lengths, the longer of saidsprings having an upper portion for engagement with said latchingdevice, the tip of the shorter of said springs tensionally engaging thelonger of said springs, said springs being wholly spaced apart exceptfor said engagement of said tip.

WINFORD G. MILNE. REGINALD E. JONES.

No references cited.

